Blow molding: Main types and technologies explained

Source：PET Technologies Release Date：2025-07-09 54

Food & BeveragePackaging Equipment & Materials Packaging

This article from PET Technologies discusses the blow molding process and how plastic containers are made using different methods.

If you were to describe PET Technologies, you could probably say that PET Technologies is a manufacturer of blow molding equipment for PET bottles. Some might be a bit more specific and say PET Technologies is a manufacturer of two-stage stretch blow molding machines for PET bottle production.

But what do these words actually mean? What is "two-stage"? What is "blow molding"? Today, let's dive into the world of blow molding to understand what it is, what types exist, and how plastic containers are made using different methods.

Definition of blow molding

According to Collins Dictionary: "Blow molding is a process for forming plastic objects in which plastic is melted, put in a mold, and then shaped by having compressed air blown into it."

Blow molding is all about creating hollow plastic parts, such as bottles, containers, and tanks. The process uses heat to soften plastic, shaping it into a mold using air pressure. It’s an essential technology that made mass production of plastic bottles and packaging possible - from the water bottle you drink from, to the detergent bottle in your laundry room.

There are several different types of blow molding processes, each with its own unique characteristics and applications.

The three main types are:

Let’s take a closer look at each of them.

1. Extrusion Blow Molding (EBM)

In this process, plastic is first melted and then extruded - meaning pushed - through a die to form a hollow tube called a parison. Once the parison reaches the right length, it is clamped inside a cooled mold. Compressed air is then blown into the parison, pressing the plastic outward against the mold walls and giving it its final shape. After cooling, the mold opens and the finished product is ejected.

Typical Products Made with EBM:

Milk jugs
Detergent bottles
Automotive ducts and tanks

Key Advantages of EBM:

Well-suited for making large, hollow parts
Handles a variety of plastics (HDPE, PP, etc.)
Can create complex shapes with handles or wide mouths

Limitations:

Not as precise in wall thickness control compared to other methods
Not the preferred method for PET bottles, which require higher clarity and strength

2. Injection Blow Molding (IBM)

Injection blow molding (IBM) combines two main steps: injection molding and blow molding. First, a preform - a small, thick-walled tube - is created by injecting melted plastic into a mold around a core rod. Next, the still-warm preform is transferred to a blow mold, where compressed air inflates it into the final shape. This method is widely used for making small, high-precision containers where uniformity is important. IBM typically works with plastics such as polypropylene (PP), polyethylene (PE), and sometimes polyethylene terephthalate (PET), depending on the application.

Typical Products Made with IBM:

Pharmaceutical bottles
Cosmetic containers
Small personal care products (travel-size bottles, etc.)

Key Advantages of Injection Blow Molding (IBM):

Produces bottles with very consistent dimensions
Ideal for small and medium-sized containers

Limitations of Injection Blow Molding (IBM):

Not suitable for large containers or high-volume beverage production
Slower cycle times compared to extrusion blow molding for bigger parts

3. Stretch Blow Molding (SBM)

Now we come to stretch blow molding - the type of blow molding technology that PET Technologies specializes in. Stretch blow molding is a process designed specifically for producing lightweight and durable PET bottles, widely used in the beverage, food and other industries.

In stretch blow molding, the plastic preform is first heated to the right temperature. Then, inside the blow mold, it is mechanically stretched (usually by a rod) and simultaneously blown with compressed air to take the shape of the mold. This stretching step is what gives PET bottles their excellent mechanical strength, clarity, and reduced material weight compared to other blow-molded containers.

The two main types of stretch blow molding processes:

One-Stage Stretch Blow Molding - the preform is injection molded, conditioned (cooled and reheated if necessary), stretched, and blown into a bottle — all in a single machine. This method is often used for small to medium production volumes or specialty bottle shapes.
Two-Stage Stretch Blow Molding - the preform is produced separately, stored or transported if needed, and later reheated and blown into bottles using a blow molding machine. This is the method used in PET Technologies blow molding machines. Those machines are ideal for high-speed, high-volume PET bottle production. This approach provides greater flexibility in preform sourcing, ensures faster production speeds, and delivers highly consistent bottle quality.

Typical Products Made with SBM:

Mineral water bottles
Soft drink bottles
Juice and dairy packaging
Edible oil bottles

Key Advantages of Stretch Blow Molding (SBM):

Lightweight bottles without compromising durability
High production speeds
Wide flexibility in bottle design
Bottle strength and clarity due to the stretching process

Limitations of Stretch Blow Molding (SBM):

Primarily limited to PET and a few specialty plastics
Requires preform sourcing or in-house production

PET Technologies will be exhibiting at Drinktec 2025, the world’s leading trade fair for the beverage and liquid food industry, from September 15-19 in Messe München. The company will be at Booth C6-461 with:

Live technology showcases – Blow molding machine, demonstrating its power and precision.
Hands-on customization experience – Discover how the company tailors molds and solutions to specific needs.
Expert strategy sessions with the company's specialists
Live technology showcases
Hands-on customization experience